Method to Manage Path Failure Thresholds

ABSTRACT

A failure threshold host command that provides a host with the capability to tune a storage controller path failure threshold based on the host application performance requirements. The failure threshold host command comprises path failure threshold rules that the storage controller uses to determine when a CHPid has reached a failed state condition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to the field of computers andsimilar technologies, and in particular to managing path failurethresholds within computer system environments.

2. Description of the Related Art

Computing devices generate information. It is known in the art to storesuch information using a plurality of data storage devices disposed inan automated data storage system. An originating host computer may be incommunication with a storage controller using a plurality ofcommunication paths.

Using prior art methods, when a host computer detects a path failureduring I/O to a storage device the host computer begins a pathverification protocol. The host computer typically sends pathverification commands to the device through each logical path recited ina device path mask. If the data returned in one of the path verificationcommands does not match the expected result, or the host pathverification command times out, the host removes that logical path fromthe device path mask. At the completion of the path verificationprocess, the device path mask may or may not still include the failedlogical path.

The path verification process can become extremely time consuming if I/Ofailures are detected for multiple logical control units within thefailure window of the several logical paths. As a result, a hostcomputer can expend an inordinate amount of time and processingresources executing path verification commands rather than I/O commands.As a result, data storage system performance can be degraded.

In large, enterprise data processing system environments, a system 390type host or other hosts that attach to a storage control unit are oftenuse a channel path identifier (CHPid) operation to physically connect toa storage controller host adapter port directly to an input port of aswitch. From the switch, the input port can be zoned to go to one ormore output ports of the switch. The output port of a switch can beconnected to a storage controller port. A host may have configuredseveral CHPids to access different storage controller ports throughdirect or switch connection.

Through a physical connection between a CHPid and one or more inputports of a storage controller, a host establishes logical paths tocommunicate with a storage controller. A host may establish one or morelogical paths per each logical control unit (LCU) of a storagecontroller. An LCU is the entity that contains a plurality of devices(e.g., up to 256 devices) to which a host accesses to perform inputoutput (I/O) operations. To access a device from different logical pathsof the same CHPid or several CHPids, it is known for a host to group upto eight logical paths into one path group.

SUMMARY OF THE INVENTION

In accordance with the present invention, a failure threshold hostcommand is set forth which provides a host with the capability to tune astorage controller path failure threshold based on the host applicationperformance requirements. The failure threshold host command comprisespath failure threshold rules that the storage controller uses todetermine when a CHPid has reached a failed state condition.

More specifically, in one embodiment, the invention relates to a methodto minimize performance degradation during communication path failure ina data processing system, the data processing system comprising a hostcomputer, a storage controller and a plurality of physical paths incommunication with the host computer and the storage controller. Themethod includes establishing a threshold communication path error ratevia a failure threshold command; determining an (i)th actualcommunication path error rate for an (i)th physical communication path,wherein said (i)th physical communication path is one of said pluralityof physical communication paths in communication with said host computerand said storage controller; discontinuing use of said (i)th physicalcommunication path if said (i)th actual communication path error rate isgreater than said threshold communication path error rate.

In another embodiment, the invention relates to an apparatus to minimizeperformance degradation during communication path failure in a dataprocessing system, the data processing system comprising a hostcomputer, a storage controller and a plurality of physical paths incommunication with the host computer and the storage controller. Theapparatus includes means for establishing a threshold communication patherror rate via a failure threshold command; means for determining an(i)th actual communication path error rate for an (i)th physicalcommunication path, wherein said (i)th physical communication path isone of said plurality of physical communication paths in communicationwith said host computer and said storage controller; means fordiscontinuing use of said (i)th physical communication path if said(i)th actual communication path error rate is greater than saidthreshold communication path error rate.

In another embodiment, the invention relates to a data processing systemcomprising a host computer, a storage controller; a plurality ofphysical paths in communication with the host computer and the storagecontroller; and, a system for minimizing performance degradation duringcommunication path failure in a data processing system. The systemcomprises instructions for: establishing a threshold communication patherror rate via a failure threshold command; determining an (i)th actualcommunication path error rate for an (i)th physical communication path,wherein said (i)th physical communication path is one of said pluralityof physical communication paths in communication with said host computerand said storage controller; discontinuing use of said (i)th physicalcommunication path if said (i)th actual communication path error rate isgreater than said threshold communication path error rate.

The above, as well as additional purposes, features, and advantages ofthe present invention will become apparent in the following detailedwritten description.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asa preferred mode of use, further purposes and advantages thereof, willbest be understood by reference to the following detailed description ofan illustrative embodiment when read in conjunction with theaccompanying drawings, where:

FIG. 1 is a block diagram showing a host computer in communication witha data storage system;

FIG. 2 is a block diagram showing a host computer communication pathmanager;

FIG. 3 is a block diagram showing a host computer in communication witha storage controller via a fabric comprising one or more switches; and

FIG. 4 is a flow chart an operation to minimize performance degradationduring communication path failure.

DETAILED DESCRIPTION

This invention is described in preferred embodiments in the followingdescription with reference to the Figures, in which like numbersrepresent the same or similar elements. Reference throughout thisspecification to “one embodiment,” “an embodiment,” or similar languagemeans that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the present invention. Thus, appearances of the phrases “in oneembodiment,” “in an embodiment,” and similar language throughout thisspecification may, but do not necessarily, all refer to the sameembodiment.

The described features, structures, or characteristics of the inventionmay be combined in any suitable manner in one or more embodiments. Inthe following description, numerous specific details are recited toprovide a thorough understanding of embodiments of the invention. Oneskilled in the relevant art will recognize, however, that the inventionmay be practiced without one or more of the specific details, or withother methods, components, materials, and so forth. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the invention.

Referring now to FIG. 1, a data processing system 100 comprises datastorage system 110 and one or more host computers 112 (also referred toas hosts). The storage system 110 is in communication with host computer112 via physical communication paths 114 a, 114 b. Communication paths114 a, 114 b each comprise a physical communication link, where thatphysical communication link can be configured to comprise up to 256logical pathways. The illustrated embodiment shows a single hostcomputer. In other embodiments, data storage system 110 may be incommunication with a plurality of host computers.

Although the system is described in terms of a storage control unit or“controller” and logical storage subsystems (LSS), the system may beimplemented with other devices as well. The storage system 110 includesa storage system such as those available from International BusinessMachines under the trade designation IBM DS6000 or DS8000. In certainembodiments, the storage system 110 includes two storage controllers 120a and 120 b, storage devices 122, such as hard disk drivers (HDDs). Incertain embodiments, the storage system can further include aninterface, such as an IBM Enterprise Storage Server Network Interface(ESSNI) or other interface.

The host 112 is coupled to the storage controller via appropriateconnections through which commands, queries, response and otherinformation are exchanged. The storage controller 120 may be configuredwith one or more logical storage subsystems (LSSs) 132 (e.g., LSS 0, LSS1, . . . LSS n). Each LSS is assigned one or more storage devices 132.

The host computer 112 includes provision for execution of a failurethreshold host command 160. The failure threshold host command 160enables a host 112 to provide path failure threshold rules to determinewhen a CHPid has reached a failed state condition. The failure thresholdhost command 160 includes parameters that contain the path failurethreshold rules. The storage controller 120 uses the path failurethreshold rules to determine when a CHPid has reached failed state. Thethreshold rules are maintained in storage controller CHPid informationdata structures.

More specifically, the failure threshold host command 160 enables thehost 112 to have control over path failures detected by the storagecontroller. Furthermore, the failure threshold host command enables thehost to decide to setup the threshold rules equally for all CHPid,equally for all CHPid that comprised a path group, differently for eachCHPid, or a combination based on the number of paths available at thetime of the paths failures.

The threshold rules defined by the failure threshold host command arebased on the application performance desired. Therefore, the failurethreshold host command enables a host to set forth tight threshold rulesfor high performance applications, as well as a different threshold rulefor medium performance applications, and a very different threshold rulefor applications that do not care about performance, but want the job tobe completed. The threshold rule should indicate the number of pathfailures within a defined failure window that would trigger a CHPidfailure state condition.

The host 112 could issue the new command as often as it needs based onthe applications performance requirements. Once the new commandcompletes successfully, the new path failure threshold rules wouldimmediately take effect on the storage controller.

Referring to FIG. 2, the host computer 112 comprises a computer system,such as a mainframe, personal computer, workstation, and combinationsthereof, including an operating system such as Windows, AIX, Unix, MVS,LINUX, etc. (Windows is a registered trademark of Microsoft Corporation;AIX is a registered trademark and MVS is a trademark of IBM Corporation;and UNIX is a registered trademark in the United States and othercountries licensed exclusively through The Open Group.) The hostcomputer 112 can further include a storage management program 210. Thestorage management program in the host computer 112 may include thefunctionality of storage management type programs known in the art thatmanage the transfer of data to a data storage and retrieval system, suchas the IBM DFSMS implemented in the IBM MVS operating system.

The host computer 390 comprises a plurality of channel path identifiers(“CHPids”) (e.g., CHPids 216 a, 216 b, 216 c, 216 d). CHPids 216 a, 216b, 216 c, 216 d, are physically interconnected to respective hostadapters within the storage controller 120. The host computer 112further comprises a communication path manager 220, where thecommunication path manager 220 is in communication with each of CHPids216. In certain embodiments, the communication path manager 220configures each of communication paths, to comprise up to 256 logicalcommunication pathways.

The host computer 112 further comprises a memory 230 (e.g., a computerreadable medium). In addition to the storage management program 210,additional instructions 232 and a physical path failure log 234 arestored on the memory 230. The instructions 232 and the storagemanagement program 210 may be loaded executed by a processor 240. Thehost computer 390 is interconnected with display device 250. The displaydevice 250 may integral with host computer 112 or may be remote fromhost computer 112. For example, the display device 250 may be located ina system administrator's office.

Referring to FIG. 3, in certain embodiments, the data storage system 110comprises a first cluster 301A and a second cluster 301B, where clusters301A and 301B may be disposed within the same housing. Each clusterincludes a host adapter portion 302, a storage controller portion 304and an input/output portion 306.

The host adapter portion 302 comprises a plurality of host adapters(HAs) 310, disposed in four host bays 312, where each host bay 312houses four host adapters 310. The data storage system 110 can includefewer than 16 host adapters. Regardless of the number of host adaptersdisposed the data storage system 110; each host adapter 310 comprises ashared resource that has equal access to processing elements (e.g.,processor 332) and cache elements (e.g., memory 334) of the data storagesystem 110.

Each host adapter 310 may comprise one or more Fibre Channel ports, oneor more FICON ports, one or more ESCON ports, or one or more SCSI ports.Each host adapter 310 is connected to both clusters 301A and 301Bthrough an interconnect bus such that each cluster can handle I/O fromany host adapter 310, and such that the storage controller portion ofeither cluster can monitor the communication path error rate for everycommunication path, physical and/or logical, interconnected with datastorage system 100.

Storage controller portion 304 includes processor 332 and memory (e.g.,a computer readable medium) 334. In certain embodiments, the memory 334comprises random access memory. In certain embodiments, memory 334comprises non-volatile memory. The storage controller portion 304 canfurther include instructions 338 as well as a physical communicationpath failure log 339 stored within the computer readable medium.

Storage controller portion 304 further comprises communication pathmanager 336. In certain embodiments, communication path manager 336comprises an embedded device disposed in storage controller portion 304.In other embodiments, communication path manager 336 comprises computerreadable program code (such as the instructions 338) written to thememory 334. The processor 332 executes instructions 338 to implement thesteps of the method for minimizing performance degradation.

The I/O portion 306 comprises a plurality of device adapters 350.

In certain embodiments, one or more host adapters, a storage controllerportion 304, and one or more device adapters, are packaged together on asingle card disposed in a data storage system. Similarly, in certainembodiments, one or more host adapters, a storage controller portion304, and one or more device adapters, are disposed on another carddisposed in the data storage system. In these embodiments, the storagesystem 110 includes two cards interconnected with a plurality of datastorage devices.

In the embodiment shown in FIGS. 1-3, sixteen data storage devices areorganized into two arrays (array A and array B). In other embodiments, adata storage system can include fewer (i.e., a single storage array) ormore than two storage device arrays. Each storage array appears to ahost computer as one or more logical devices (i.e., as a logical storagesystem (LSS)).

In certain embodiments, one or more of the data storage devices comprisea plurality of hard disk drive units, such as plurality of disk driveunits 132. In certain embodiments, the arrays A and B may utilize a RAIDprotocol. In certain embodiments, the arrays A and B may comprise whatis sometimes referred to as a JBOD array, i.e. “Just a Bunch Of Disks”where the array is not configured according to RAID. As those skilled inthe art will appreciate, a RAID (Redundant Array of Independent Disks)rank comprises independent disk drives configured in an array of diskdrives to obtain performance, capacity and/or reliability that exceedsthat of a single large drive.

In certain embodiments, the storage system 110 may be in communicationwith a service center (not shown). In certain embodiments, the storagesystem 110 provides information relating to system performance toservice center at pre-determined time intervals. In certain embodiments,the storage system 110 immediately provides error messages to servicecenter upon detection of a physical communication path performancedegradation.

The data storage system includes provision for minimizing performancedegradation during communication path failure in a data processingsystem. FIG. 4 shows a flow chart of the operation for minimizingperformance degradation during communication path failure via a failurethreshold host command.

In step 420, the method establishes a threshold communication path errorrate via the failure threshold host command. In certain embodiments, thethreshold communication path error rate of step 420 comprises themaximum number of I/O failures allowable during a specified timeinterval.

In certain embodiments, a threshold communication path error rate is setby the operator of each host computer. If data storage system 110 is incommunication with a plurality of host computers, each of the hostcomputers could specify a different and unique threshold communicationpath error rate via respective failure threshold host commands. Incertain embodiments, the threshold communication path error rate of step420 is set by the operator of the data storage system 110 or storagecontroller 120.

In step 430, the method selects an (i)th communication path, where (i)is initially set to one. In certain embodiments, step 430 is performedby a host computer such as host computer 112. In certain embodiments,step 430 is performed by a communication path manager, such ascommunication path manager 220, disposed in the host computer.

In certain embodiments, step 430 is performed by a storage controllersuch as storage controller 120. In certain embodiments, step 430 isperformed by a path management function the storage controller 120. Incertain embodiments, step 430 is performed by both clusters, such asclusters 301A and 301B, disposed in a data storage system 112. Incertain embodiments, step 430 is performed by a path management functiondisposed in cluster 301A and/or by a path management function disposedin cluster 301B.

In step 440, the method determines an (i)th actual communication patherror rate for an (i)th physical communication path. In certainembodiments, step 440 is performed by the host computer 112. In certainembodiments, step 440 is performed by a communication path manager 220.In certain embodiments, step 440 is performed by the storage controller120. In certain embodiments, step 440 is performed by a path managementfunction disposed in the storage controller of step 410. In certainembodiments, step 440 is performed by both clusters, such as clusters301A and 301B, disposed in the data storage system 110. In certainembodiments, step 440 is performed by a path management functiondisposed in cluster 301A and/or by a path management function disposedin cluster 301B.

In step 450, the method determines if the (i)th actual communicationpath error rate of step 440 is greater than the threshold communicationpath error rate set via the failure threshold host command of step 420.In certain embodiments, step 450 is performed by the host computer 112.In certain embodiments, step 450 is performed by the communication pathmanager 220. In certain embodiments, step 450 is performed by thestorage controller 120. In certain embodiments, step 450 is performed bya path management function disposed in the storage controller 120. Incertain embodiments, step 450 is performed by both clusters, such asclusters 301A and 301B. In certain embodiments, step 450 is performed bya path management function disposed in cluster 301A and/or by a pathmanagement function disposed in cluster 301B.

If the method determines in step 450 that the (i)th actual communicationpath error rate of step 440 is greater than the threshold communicationpath error rate of step 420, then the method transitions from step 450to step 460 where the method discontinues using the (i)th physicalcommunication path. In certain embodiments, the (i)th physicalcommunication path may comprise up to 256 logical communication paths.It may be the case that only one of those 256 logical communicationpaths has failed. By discontinuing use of the entire physicalcommunication path, the use of operable logical communication paths isalso discontinued. However, discontinuing use of the (i)th physicalcommunication path avoids expending host computer processing time toidentify the one or more failed logical communication paths. Repair ofthe physical connection can be deferred until a more convenient timewhen such repair causes no impact on data storage system performance.

For example, the determination that an (i)th actual communication patherror rate exceeds a threshold communication path error rate may be madeat a first time, but the identification of and/or repair of the one ormore degraded logical communication paths configured by the (i)thphysical communication path can be made at a second time, where the timeinterval between the first time, i.e. failure detection, and the secondtime, i.e. degraded logical path determination and repair, can be hours.In certain embodiments, the time interval between the first time and thesecond time can be as great as 24 hours.

In certain embodiments, step 460 is performed by the host computer 112.In certain embodiments, step 460 is performed by the communication pathmanager 220 disposed in the host computer 112. In certain embodiments,step 460 is performed by the storage controller 120. In certainembodiments, step 460 is performed by a path management functiondisposed in the storage controller 120. In certain embodiments, step 460is performed by both clusters, such as clusters 301A and 301B. Incertain embodiments, step 460 is performed by a path management functiondisposed in cluster 301A and/or by a path management function disposedin cluster 301B.

In step 470, the method displays an error message on a display device.In certain embodiments, step 470 further comprises making a log entry toa physical communication path failure log, such as log 234. In certainembodiments, step 470 further comprises providing the physicalcommunication path failure log entry to a service center. In certainembodiments, step 470 is performed by the host computer 112, where theerror message is displayed on the display device 250. In certainembodiments, step 470 is performed by a communication path manager 220,where the error message is displayed on the display device 250. Incertain embodiments, step 470 is performed by the storage controller 120where the error message is displayed on a display device disposed in aservice center in communication with the storage controller. In certainembodiments, step 470 is performed by a path management functiondisposed in the storage controller, where the error message is displayedon a display device disposed in a service center in communication withthe storage controller. In certain embodiments, step 470 is performed byboth clusters, such as clusters 301A and 301B where if either clusterdetermines in step 450 that an (i)th actual communication path errorrate of step 440 is greater than the threshold communication path errorrate of step 420, then an error message is displayed on a displaydevice, such as a display device disposed in a service center incommunication with the data storage system. In certain embodiments, step470 is performed by a path management function disposed in cluster 301Aand/or by a path management function disposed in cluster 301B, where ifeither path management function determines in step 450 that an (i)thactual communication path error rate of step 440 is greater than thethreshold communication path error rate of step 420 an error message isdisplayed on a display device, such as a display device disposed in aservice center in communication with the data storage system.

In step 480, the method determines if an actual communication path errorrate has been determined for each of the plurality of communicationpaths. For example, if the plurality of communication paths of step 410comprise (N) communication paths, then in step 480 the method determinesif (i) equals (N). In certain embodiments, step 480 is performed by thehost computer 112. In certain embodiments, step 480 is performed by acommunication path manager 220. In certain embodiments, step 480 isperformed by the storage controller 120. In certain embodiments, step480 is performed by a path management function disposed in the storagecontroller 120. In certain embodiments, step 480 is performed by bothclusters, such as clusters 301A and 301B, disposed in a data storagesystem. In certain embodiments, step 480 is performed by a pathmanagement function disposed in cluster 301A and/or by a path managementfunction disposed in cluster 301B.

If the method determines in step 480 that an actual communication patherror rate has not been determined for each of the plurality ofcommunication paths of the data storage system, then the methodtransitions from step 480 to step 490 where the method increments (i) byunity, and transitions from step 490 to step 440 and continues asdescribed herein. In certain embodiments, step 490 is performed by thehost computer 112. In certain embodiments, step 490 is performed by acommunication path manager 220. In certain embodiments, step 490 isperformed by the storage controller 120. In certain embodiments, step490 is performed by a path management function disposed in the storagecontroller 120. In certain embodiments, step 490 is performed by bothclusters, such as clusters 301A and 301B, disposed in a data storagesystem 110. In certain embodiments, step 490 is performed by a pathmanagement function disposed in cluster 301A and/or by a path managementfunction disposed in cluster 301B.

If the method determines in step 480 that an actual communication patherror rate has been determined for each of the plurality ofcommunication paths, then the method transitions from step 480 to step430 and continues as described herein. In certain embodiments, afterdetermining in step 480 that an actual communication path error rate hasbeen determined for each of the plurality of communication paths, themethod transition to, and performs, step 430 after a time intervaldefined by the threshold communication path error rate of step 420.

As an example, if the threshold communication path error rate is basedupon a number of I/O failures per minute, then the method performs step430 within about one minute after transitioning from step 480.Similarly, if the threshold communication path error rate is based upona number of I/O failures per hour, then the method performs step 430within about one hour after transitioning from step 480. If thethreshold communication path error rate is based upon a number of I/Ofailures per day, then the method performs step 430 within about one dayafter transitioning from step 480.

In certain embodiments, individual steps recited in FIG. 4 may becombined, eliminated, or reordered.

In certain embodiments, the data storage system 100 includesinstructions, residing in computer readable medium. The instructions maybe executed by a processor to perform one or more of steps 420, 430,440, 450, 460, 470, 480, and 490. In other embodiments, the instructionsmay reside in any other computer program product, where thoseinstructions are executed by a computer external to, or internal to,data storage system 100 to perform one or more of steps 420, 430, 440,450, 460, 470, 480, and 490. In either case, the instructions may bestored on computer readable medium comprising, for example, a magneticinformation storage medium, an optical information storage medium, anelectronic information storage medium, and the like. By “electronicstorage media,” include, for example, one or more devices, such as aPROM, EPROM, EEPROM, Flash PROM, compactflash, smartmedia, and the like.

It is important to note that while the present invention has beendescribed in the context of a fully functioning data processing system,those of ordinary skill in the art will appreciate that the processes ofthe present invention are capable of being distributed in the form of acomputer program product of a computer-readable medium havingcomputer-readable code comprising instructions and a variety of formsand that the present invention applies regardless of the particular typeof signal bearing media actually used to carry out the distribution.Examples of computer readable media include recordable-type media suchas a floppy disk, a hard disk drive, a RAM, and CD-ROMs andtransmission-type media such as digital and analog communication links.

The description of the present invention has been presented for purposesof illustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the art. Theembodiment was chosen and described in order to best explain theprinciples of the invention, the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated. Moreover, although described above withrespect to methods and systems, the need in the art may also be met witha computer program product containing instructions for executingnon-device specific server commands in a storage control unit.

While the present invention has been particularly shown and describedwith reference to a preferred embodiment, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention.Furthermore, as used in the specification and the appended claims, theterm “computer” or “system” or “computer system” or “computing device”includes any data processing system including, but not limited to,personal computers, servers, workstations, network computers, main framecomputers, routers, switches, Personal Digital Assistants (PDAs),telephones, and any other system capable of processing, transmitting,receiving, capturing and/or storing data.

1. A method to minimize performance degradation during communicationpath failure in a data processing system, the data processing systemcomprising a host computer, a storage controller and a plurality ofphysical paths in communication with the host computer and the storagecontroller, the method comprising: establishing a thresholdcommunication path error rate via a failure threshold command;determining an (i)th actual communication path error rate for an (i)thphysical communication path, wherein said (i)th physical communicationpath is one of said plurality of physical communication paths incommunication with said host computer and said storage controller;discontinuing use of said (i)th physical communication path if said(i)th actual communication path error rate is greater than saidthreshold communication path error rate.
 2. The method of claim 1wherein: the host computer comprises at least one channel pathidentifier (CHPid); and, the failure threshold command enables provisionof path failure threshold rules to determine when a CHPid has reached afailed state condition.
 3. The method of claim 2 wherein: the failurethreshold command includes parameters that contain path failurethreshold rules; and, the storage controller uses the path failurethreshold rules to determine when a CHPid has reached a failed state. 4.The method of claim 3 wherein: the path failure threshold rules aremaintained in a storage controller CHPid information data structure. 5.The method of claim 3 wherein: the failure threshold command enables ahost to have control over path failures detected by the storagecontroller; and, the failure threshold command enables path failurethreshold rules to be set up equally for all CHPid, equally for allCHPid that comprise a path group, differently for each CHPid, or acombination based on a number of paths available at a time of a pathfailure detection.
 6. The method of claim 3 wherein: the threshold rulesdefined by the failure threshold host command are based on desiredapplication performance.
 7. The method of claim 6 wherein: the failurethreshold rule indicates a number of path failures within a definedfailure window that would trigger a CHPid failure state condition.
 8. Anapparatus to minimize performance degradation during communication pathfailure in a data processing system, the data processing systemcomprising a host computer, a storage controller and a plurality ofphysical paths in communication with the host computer and the storagecontroller, the apparatus comprising: means for establishing a thresholdcommunication path error rate via a failure threshold command; means fordetermining an (i)th actual communication path error rate for an (i)thphysical communication path, wherein said (i)th physical communicationpath is one of said plurality of physical communication paths incommunication with said host computer and said storage controller; meansfor discontinuing use of said (i)th physical communication path if said(i)th actual communication path error rate is greater than saidthreshold communication path error rate.
 9. The apparatus of claim 8wherein: the host computer comprises at least one channel pathidentifier (CHPid); and, the failure threshold command enables provisionof path failure threshold rules to determine when a CHPid has reached afailed state condition.
 10. The apparatus of claim 9 wherein: thefailure threshold command includes parameters that contain path failurethreshold rules; and, the storage controller uses the path failurethreshold rules to determine when a CHPid has reached a failed state.11. The apparatus of claim 10 wherein: the path failure threshold rulesare maintained in a storage controller CHPid information data structure.12. The apparatus of claim 10 wherein: the failure threshold commandcontrol over path failures detected by the storage controller; and, thefailure threshold command enables path failure threshold rules to be setup equally for all CHPid, equally for all CHPid that comprise a pathgroup, differently for each CHPid, or a combination based on a number ofpaths available at a time of a path failure detection.
 13. The apparatusof claim 10 wherein: the threshold rules defined by the failurethreshold host command are based on desired application performance. 14.The apparatus of claim 13 wherein: the failure threshold rule indicatesa number of path failures within a defined failure window that wouldtrigger a CHPid failure state condition.
 15. A data processing systemcomprising a host computer, a storage controller; a plurality ofphysical paths in communication with the host computer and the storagecontroller; and, a system for minimizing performance degradation duringcommunication path failure in a data processing system, the systemcomprising instructions for: establishing a threshold communication patherror rate via a failure threshold command; determining an (i)th actualcommunication path error rate for an (i)th physical communication path,wherein said (i)th physical communication path is one of said pluralityof physical communication paths in communication with said host computerand said storage controller; discontinuing use of said (i)th physicalcommunication path if said (i)th actual communication path error rate isgreater than said threshold communication path error rate.
 16. The dataprocessing system of claim 15 wherein: the host computer comprises atleast one channel path identifier (CHPid); and, the failure thresholdcommand enables provision of path failure threshold rules to determinewhen a CHPid has reached a failed state condition.
 17. The dataprocessing system of claim 16 wherein: the failure threshold commandincludes parameters that contain path failure threshold rules; and, thestorage controller uses the path failure threshold rules to determinewhen a CHPid has reached a failed state.
 18. The data processing systemof claim 17 wherein: the path failure threshold rules are maintained ina storage controller CHPid information data structure.
 19. The dataprocessing system of claim 17 wherein: the failure threshold commandcontrol over path failures detected by the storage controller; and, thefailure threshold command enables path failure threshold rules to be setup equally for all CHPid, equally for all CHPid that comprise a pathgroup, differently for each CHPid, or a combination based on a number ofpaths available at a time of a path failure detection.
 20. The dataprocessing system of claim 19 wherein: the threshold rules defined bythe failure threshold host command are based on desired applicationperformance.
 21. The data processing system of claim C6 wherein: thefailure threshold rule indicates a number of path failures within adefined failure window that would trigger a CHPid failure statecondition.